In, e.g., a conventional facsimile apparatus that can read a color image as an image reading apparatus, R, G, and B light sources are time-divisionally turned on to color-separate a document image, image data of respective color components line-sequentially read by a single read sensor are temporarily stored in buffer memories, a masking process is done in synchronism with data input of the last color B of R, G, and B colors, and a color conversion process (RGB/CMYK conversion process) is done to output data.
However, since the conventional image reading apparatus executes the masking process in synchronism with input (image read) of the last color, the pixel processing rate (image processing speed) in the masking process and subsequent processes must be 3 to 4 times higher than the rate (image read speed) of the input stage, and an apparatus which cannot process data at high speed cannot often fully utilize the performance of the read sensor.
In an image reading apparatus which reads an image by scanning a document such as a book using a hand scanner unit which includes a read sensor and is detachable from the apparatus main body, an image begins to be read in accordance with movement detected by a movement sensor provided to the hand scanner unit. However, when the moving speed is high, read errors occur.
Furthermore, when the processing rate (image processing speed) in the masking process and subsequent processes is set to be high, the performance of the read sensor can be fully utilized, but the circuit scale of an image processor that attains high-speed operations increases.
Hence, a technique that can improve the image read speed without setting a high image processing speed for the masking process and subsequent processes is demanded.